Three international companies investigated this complex issue, setting new horizons in optical science along the way. Their crowning achievement is a world first – an effects-measuring instrument that dramatically cuts the time and cost of formulating and spraying.

Few things turn a car owner's pride to anger faster than a botched paint job. Yet the body-shop may be equally adamant that it sprayed the repaired area with an appropriate coating colour. This perception gap also bedevils automotive suppliers who too often must re-spray new car parts, like panels, bumpers and dashboard fascias.

The problem is in the paint. Metallic, pearlescent and other interference effects that add appeal to some 75% of new cars have been a source of expensive frustration since special effect coatings were introduced in the 1970s.

A host of factors, including lighting and viewing angles, greatly complicate the attempts of colour formulators and car painters alike to create and mix undetectable finishes. Years of work are spent analysing and formulating repair paints. Yet even then, a car-body restoration that is rendered invisible in the repair-shop may be glaringly obvious when the car emerges into daylight.

This laborious, costly situation led three international companies to participate in the EUREKA E! 3037 TARBAM project. Their aim was to develop the holy grail of the car coatings industry... an instrument to analyse and measure the texture of effect coatings. This capability would reduce significantly the long, expensive lead times spent in creating simulation coatings, and virtually eliminate the risk of shop-floor mis-matches.

The 4.7 million euro project was proposed and led by Akzo Nobel Car Refinishes b.v. (ANCR), one of the world’s biggest suppliers of coatings to car-body repair shops. The Netherlands-based company turned to EUREKA for high-level management support and official acceptance, including fast-track financing from public funds. Additionally, the project needed access to scientific and academic disciplines.

“EUREKA helped us to convince people inside and outside our company that we were working towards new technologies that would be recognised by independent professionals,” says Roel Gottenbos, ANCR’s Manager Technology Center Colorimetry, who was the project coordinator.

The project's title reflects the names of the three participating companies: TARBAM – Total Appearance Research BYK-Gardner, Akzo Nobel, Merck.

Trial and error

The inability to accurately define and measure effect coatings had long been a costly problem. Conventional spectrophotometers for determining solid colours cannot cope with the texture (coarseness or graininess) and glints of effect coatings. Formulators, therefore, have relied mainly on their eyes to assess finishes. And while the human eye is supreme at making comparisons, this approach entails a lengthy, painstaking process to create visually acceptable car repair paints that can be mixed readily from a manageable range of pigments and additives.

Even then, trial and error is the usual method to fine tune coating mixes on the shop floor – often with unwanted, costly results. As well as lighting and viewing angle problems, a slight difference in spray pressure can change the orientation of aluminium flakes in a metallic paint to produce what is perceived as a different colour tone.

After five years of inter-company cooperation under EUREKA, ANCR and its two German-based partners exceeded their original aims by developing a new technology and producing a unique instrument that measures texture and color simultaneously. This world-first will enable formulators and spray-shops to reduce spray-outs and mis-matches.

One of the first issues facing the project's five task-teams was the need for a terminology to describe the appearance of effect paints. The lack of a standard nomenclature for the industry was central to the mis-match predicament.

Psycho physics

ANCR shared the work of producing a nomenclature, as well as analysing coatings and devising formulations, with Merck Chemicals, a major global supplier of effect pigments, and part of the worldwide Merck chemicals and pharmaceuticals group. This phase was part of psychophysical observation where experienced staff visually assessed the relation between original car colour and repair colour by viewing small sprayed panels under various conditions.

Mathematical values could be then assigned, correlating visual perception with physical variables and quantities. This modelling has produced a vast library of values that enables specialised software to compute formulations for optimal car repair coatings.

In all, ANCR has amassed a database of more than 100,000 colours. However, according to Roel Gottenbos, even if car manufacturers were willing to disclose their coating formulations, the refinish market would still need to formulate its own finishes because factors such as paint binder-systems can produce big colour differences for each coating colour.

Winning the impossible challenge

The assessment and cataloguing of coatings provided BYK-Gardner GmbH, the other project participant, with parameters for developing an instrument that could look into the depths of effect paints and measure their visual texture. The company, a division of Altana group's BYK-Chemie division, also worked on developing a more sophisticated colour spectrophotometer. The outline plan for the TARBAM project envisaged the development of two instruments for use by formulators and shop-floor personnel.

But as the project progressed, it was felt that the colour and effect measuring functions should be integrated in one instrument. This would greatly streamline operations by the customer. Although the idea sounded simple, it presented the TARBAM device-development team with a problem so complex that some experts dismissed it as impossible. Indeed, more people were brought in to work on this development, which became an important spin-off activity of the overall project.

The instrument is the BYK-mac, a robust, hand-held device that is being marketed to the OEM sector. Roel Gottenbos says that ANCR expects the BYK-mac will enable the number of spray-outs for creating new formulations to be reduced by around 20%, or some 50,000 panels a year. ANCR is considering including the device in a package for the car-body repair market. The outlook is said to be highly promising for sales of many thousands of units worldwide.

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